1. Field of the Invention
The present invention relates generally to subsea pipeline connections and more particularly to subsea branch and termination connection points where a subsea connection jumper would be used.
2. Background Art
A marine pipeline system may consist of many branch or tributary pipelines, which feed the product into a common main pipeline or trunkline. The pipeline system may have many mid-line connection points. The mid-line connection points have connection hubs where connections may be made to join the pipeline, or pipelines, to production infrastructure. For subsea marine pipelines this is frequently done with connection jumpers which span between two end points to complete a connection. The mid-line connection points also have pipeline end sleds or manifolds to assist in connecting a jumper to the connection hub of the mid-line connection point.
A common type of pipeline end sled has a platform or other support structure for landing a connection jumper so that the connection jumper can be mated to the connection hub of the mid-line connection point. The pipeline end sled may also have guideposts for aligning the landing of the jumper connector. The guideposts also act as an anchor for the forces required to pull in a jumper to mate with the connection hub of the mid-line connection point.
When mating a connection jumper to a mid-line connection point, the connection jumper must be specially manufactured and installed to connect the pipeline to infrastructure or another pipeline. The connection jumper must be manufactured such that it spans between the connection hubs and mimics the geometrical orientation of the two hubs. When the connection jumper is manufactured it must be positioned or "rigged" precisely so that it can be lowered to the seafloor and landed on the pipeline end sled or manifold so that a connection can be made.
The process of manufacturing and landing a connection jumper is more difficult if the pipeline end sleds and guideposts are not in the desired vertical position. When a pipeline is installed subsea, the process inherently introduces torsion into the pipeline. The pipeline and any associated connection points may then rotate to alleviate all or part of this torsion. When the pipeline end sled is located along the pipeline, this pipe rotation may cause the platform or other support structure of the sled to be oriented up to plus or minus 25 degrees from the desired vertical position. Accordingly, a future tie-in to a rotated pipeline sled will have to overcome any roll found in the platform or other support structure of the pipeline sled.
The present state of the art requires that the connection jumper be manufactured to mimic the relative distance, elevation, roll, pitch, and yaw between the hubs. Thus, a need exists for less restrictive manufacture of the connection jumper and less difficulty landing the connection jumper.
Moreover, current state of the art requires pipeline installation contractors to land the pipeline and mid-line connection points (including the pipeline end sleds) on the sea floor within a particular roll angle window relative to horizontal. In order to accomplish this task, great care and time are required while using buoyancy modules to counteract the tendency of the pipe to roll as it is laid. Thus, a need also exists for less restrictive measures for laying pipeline to the sea floor.